Not Applicable.
The present invention relates generally to steel production, and more particularly, but not necessarily entirely, to a steel heating furnace with particular use in reheating previously cast steel.
In the steel making industry, it is known to produce steel and store it in slabs in sizes required by the provider. This is often accomplished by (i) dispensing newly formed steel from a continuous caster in the form of slabs, during which the steel slabs unavoidably cool to a temperature below the desired working temperature of the steel, (ii) feeding the slabs of steel through a reheat furnace to thereby heat the steel slab to a working temperature, and then (iii) compressively rolling the steel slabs into a reduced thickness. This type of steelmaking system is thus summarized briefly as comprising a caster, reheat furnace, and roll line, utilized in sequence in that order.
A newly cast continuous slab of steel is initially quite thick as it is dispensed from the caster. The slab might for example be 25.4 cm (10 inches) thick. Although the steel has a temperature of perhaps 815xc2x0 C. (1500xc2x0 F.) when it is dispensed from the caster, it generally requires a working temperature maintained above 982xc2x0 C. (1800xc2x0 F.) while it is rolled into the desired thickness. Naturally, the hotter the steel, the easier it can be rolled, such that a temperature of 2200xc2x0 F. is preferred. The newly cast steel slab can either be stored somewhere to be reheated and rolled later, or it can be heated immediately to the higher working temperature and rolled right after casting. Naturally, less energy is required to heat the steel slab from 815xc2x0 C. (1500xc2x0 F.) to a working temperature above 982xc2x0 C. (1800xc2x0 F.) directly after casting than would be required if the steel is stored temporarily after casting and allowed to cool to ambient temperature prior to rolling. It is therefore desirable, in steel casting operations, to utilize the caster, reheat furnace, and roll line in direct succession.
It is futile to attempt to roll steel unless the slab of steel is heated to a working temperature well above 982xc2x0 C. (1800xc2x0 F.), such that the temperature of all portions of the steel is maintained above 982xc2x0 C. (1800xc2x0 F.). When the steel slab is heated to the working temperature, it is fed through the rollers in the roll line, which roll and compress the steel to a reduced thickness using roll line machinery and processes known to those having ordinary skill in the field. For example, a slab of steel cast at 25.4 cm (10 inches) thick can be reheated and rolled to a reduced thickness of 0.16 cm (1/16 of an inch) or thinner.
Several attempts have been made to construct a steel heating furnace that works efficiently. Many such attempts are described in the following U.S. patents, which are incorporated herein by reference: U.S. Pat. No. 1,539,833; U.S. Pat. No. 1,791,166; U.S. Pat. No. 1,833,132; U.S. Pat. No. 2,883,172; U.S. Pat. No. 2,929,614; U.S. Pat. No. 3,770,103; U.S. Pat. No. 4,243,378; U.S. Pat. No. 5,441,407; and U.S. Pat. No. Re. 19,205.
The known steel reheat furnaces generally burn natural gas or a hydrocarbon fuel within the furnace to provide the heat. The gas or fuel combusts to form super-heated water vapor and carbon dioxide. The water vapor reacts with the steel to form a magnetic iron oxide (Fe3O4) on the surface of the steel being reheated, in the form of an undesirable crusty, abrasive surface scale. The iron oxide scale must be removed before rolling, otherwise, the iron oxide scale becomes rolled right into the steel surface during rolling and becomes a defect in the steel, such defects sometimes being referred to as xe2x80x9cpits.xe2x80x9d Sometimes slivers of the iron oxide are rolled into the steel.
The prior art reheat furnaces are not sealed from the atmosphere, and in fact have openings along their sides. To prevent the gas-burning flames from venturing through the open sides and outside the furnace, a pressure monitoring system is utilized in which the pressure within the furnace matches the surrounding atmospheric pressure. This pressure matching system of operation, when utilized in a reheat furnace having side openings, carries the risk of leaking some gas into the atmosphere because the matching pressure varies and therefore cannot be completely reliable.
Common types of reheat furnaces include a xe2x80x9cpusher furnace,xe2x80x9d a xe2x80x9cwalking beamxe2x80x9d furnace, and a xe2x80x9croller hearthxe2x80x9d or xe2x80x9ctunnelxe2x80x9d furnace. In the walking beam furnaces and in the pusher-type furnaces there is a high degree of surface contact of the steel slabs with the slab supports, particularly in the pusher-type furnaces. Such surface contact causes the slab supports to absorb heat from the steel, often undesirably scoring the slab and producing xe2x80x9ccold spotsxe2x80x9d on the steel slab. These cold spots can result in an inconsistent thickness in the rolled steel. Although the conventional roller hearth type furnace has the advantage of uniformly heating the steel slabs without damaging or marking the surface, it also has the disadvantage of causing excessive heat loss, and the rollers are highly expensive.
The prior art reheat furnaces are thus characterized by several disadvantages that are addressed by the present invention. The present invention minimizes, and in some aspects eliminates, the above-mentioned failures, and other problems, by utilizing the methods and structural features described herein.
In view of the foregoing, it will be appreciated that a steel heating furnace that can significantly reduce oxidation of the surface of the steel, and provide for a controlled atmosphere during reheating, and reduce cold spots and thus increase the consistency of thickness of rolled steel, and improve efficiency of reheating steel, and avoids damaging or marking the surface of the steel, would be a significant advancement in the art.
It is therefore an object of the present invention to provide a steel heating furnace that is simple in concept.
It is another object of the present invention to provide such a steel heating furnace that minimizes the occurrence of iron oxide forming in the surface of the steel.
It is a further object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace in which the use of hydrocarbon fuel, such as natural gas, is avoided during operation.
It is an additional object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace in which the occurrence of water vapor within the furnace is minimized.
It is yet another object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace in which a carbon monoxide atmosphere is maintained within the furnace during operation.
It is a still further object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace capable of enabling steel to be heated with an unoxidized finish.
It is an additional object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace in which steel within the furnace is more evenly heated.
The above objects and others not specifically recited are realized in a specific illustrative embodiment of a steel heating furnace, comprising:
a furnace housing for receiving steel thereinto, the furnace housing defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace; and
means for supplying carbon monoxide into the interior furnace space and maintaining a carbon monoxide atmosphere within the interior furnace space.
Another illustrative embodiment of the invention comprises:
a furnace housing for receiving steel thereinto, the furnace housing defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace; and
means for substantially sealing the furnace housing from the atmosphere.
Still another illustrative embodiment of the invention comprises:
a furnace housing for receiving steel thereinto, the furnace housing comprising sides, an entrance, and an exit opening, and wherein the furnace housing is sealed along its sides from the atmosphere and defines an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace; and
means for blocking the entrance and the exit opening of the furnace housing from the atmosphere to inhibit the entry of ambient air into the furnace housing.
Yet another illustrative embodiment of the invention comprises:
a furnace housing for receiving steel thereinto, the furnace housing having sides and defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace; and
rollers rotatably disposed within the furnace housing for supporting steel thereupon, wherein the rollers are fully confined within the furnace housing without extending beyond the sides of the furnace.
A still further illustrative embodiment of the invention comprises:
a furnace housing for receiving steel thereinto, the furnace housing defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace; and
a plurality of support roller means rotatably disposed within the furnace housing for supporting steel thereupon, wherein each support roller means comprises a series of spaced-apart, co-axial wheels.
Another illustrative embodiment of the invention comprises:
a furnace housing for receiving steel thereinto, the furnace housing defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace;
a plurality of support roller means rotatably disposed within the furnace housing for supporting steel thereupon; and
a plurality of stabilizer roller means disposed beneath, and in alignment with, the roller means, respectively.
Still another illustrative embodiment of the invention comprises a steel heating furnace, comprising:
a furnace housing for receiving steel thereinto, the furnace housing having sides and defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace; and
support rollers rotatably and removably disposed within the furnace housing for supporting steel thereupon, such that said rollers are interchangeable.
Yet another illustrative embodiment of the invention comprises:
a furnace housing for receiving steel thereinto, the furnace housing having sides and defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace;
support rollers rotatably disposed within the furnace housing for supporting steel thereupon; and
advancing means for advancing steel through the furnace housing without imparting a direct torsion driving force to the support rollers. As used herein, xe2x80x9cdirect torsion driving forcexe2x80x9d means the force imparted by direct attachment to a driven member, such as a belt or chain, by means of a sprocket, pulley, or the like. In the present invention, the support rollers are xe2x80x9cfloating,xe2x80x9d meaning that such support rollers are not driven via a sprocket, pulley, or similar component, but instead are driven only by frictional force transferred from another moving component of the system, such as the steel belt.
A still further illustrative embodiment of the invention comprises:
(a) placing the steel in a steel heating furnace such that the steel is enveloped in a carbon monoxide atmosphere; and
(b) oxidizing a portion of the carbon monoxide atmosphere, thereby generating heat and reheating the steel.
Another illustrative embodiment of the invention comprises:
(a) placing the steel in a steel heating furnace comprising
a furnace housing for receiving steel thereinto, the furnace housing having sides and defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace;
support rollers rotatably disposed within the furnace housing for supporting steel thereupon;
advancing means for advancing steel through the furnace housing without imparting a direct torsion driving force to the support rollers
(b) heating the interior furnace space and the steel placed therein; and
(c) advancing the steel through the furnace housing by imparting frictional driving force to the support rollers, which then impart frictional driving force to the steel.
Still another illustrative embodiment of the invention comprises:
(a) placing the steel in a steel heating furnace comprising:
a furnace housing for receiving steel thereinto, the furnace housing having sides and defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace;
support rollers rotatably disposed within the furnace housing for supporting steel thereupon; and
a hearth defining a floor of the interior furnace space configured for partially shielding the support rollers from heat contained in the interior furnace space;
(b) heating the interior furnace space and the steel placed therein; and
(c) advancing the steel through the furnace housing by causing the support rollers to rotate, thereby imparting frictional driving force to the steel.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by the practice of the invention without undue experimentation. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.